1. Field of the Invention
The present invention relates generally to web printing presses and more particularly to a folder for cutting a web into signatures.
2. Background Information
Web printing presses print a continuous web of material, such as paper. The continuous web then is cut in a cutting unit of a folder so as to form signatures which can then be folded or output.
U.S. Pat. No. 5,740,709 discloses a double-cut folder. The cutting cylinders do not provide a nipping action. This device is disadvantageous in that signatures may experience a stepped cut due to motion between the first and second cut.
U.S. Pat. No. 4,957,280 discloses a folder in which a web is first cut by a cutter drum, and then is pinched between a folding drum and conveyor belts. The web not cut by the first cutter drum is then cut by saw-tooth cutter blades of a second cutter device disposed on the folder drum so as to form a cut sheet. A head end of the web cut into the sheet is pushed into gaps between a plurality of clamping claws and claw seats and clamped.
The '280 patent has the disadvantages that slip may still occur in both the web direction and in a cross-web direction owing to the fact that the nip forces between the conveyor belts and the folding drum may not be sufficient. A stepped cut thus also may occur. Cut accuracy may also suffer due to a radius effect when variable thicknesses of web pass through the folder. Moreover, the '280 patent appears to require a complicated jaw-type device to maintain proper signature control. In addition, the anvil surfaces or cutter receiver may wear out over time.
Commonly-owned U.S. patent application Ser. No. 09/435,667 filed Nov. 8, 1999 (which is not necessarily prior art to the present invention) discloses a double-cut lobed belt diverter. A first cut is made with a first cutting cylinder and then a second cut by a second cutting cylinder having cutting disks. Lobed belts pass between the cutting disks to grab the cut signatures and divert the signatures into two streams. The belts grasps the lead of the signature after the second cut and thus do not help to maintain signature control during the second cut.